This invention relates to a hydraulic shock absorber in which internally sealed gas and hydraulic fluid are mutually separated and the gas pressure can be adjusted from the outside.
There are gas-liquid separation hydraulic shock absorbers in which mixing is prevented between the gas and hydraulic fluid sealed in the interior of the hydraulic shock absorber.
A device structured as shown in FIG. 4 is an example of such a hydraulic shock absorber.
An outer casing 3 is disposed coaxially around the exterior of a cylinder 1. A reservoir 6 is provided between the cylinder 1 and the outer casing 3. A gas chamber 7, which is partitioned off by a flexible bladder 4 and in which gas is sealed, is formed in the reservoir 6. The bladder 4 is formed into a cylinder, and a smaller upper end 4a and lower end 4b are fastened airtightly to the exterior of the cylinder 1 by a clamp ring 5, and are thereby sealed so as not to allow the gas pressure sealed in the interior gas chamber 7 to leak.
A reservoir chamber 8 is formed between the outer surface of the bladder 4 and outer casing 3, and the reservoir chamber 8 is communicated with an oil chamber (not shown) inside the cylinder 1, which is filled with hydraulic fluid.
When the hydraulic shock absorber is compressed, a piston rod 2 enters the cylinder 1, and an amount of hydraulic fluid equivalent to the entered volume of the piston rod flows from the oil chamber in the cylinder into the reservoir chamber 8, and the gas chamber 7 is compressed. When the hydraulic shock absorber extends, an amount of hydraulic fluid equivalent to the extending volume of the piston rod 2 flows from the reservoir chamber 8 into the oil chamber in the cylinder, and the reservoir chamber 8 expands.
Thus, while the piston rod 2 expands and contracts, hydraulic fluid enters and leaves between the oil chamber in the cylinder and the reservoir chamber 8, damping force in the hydraulic shock absorber arises as a result of resistance occurring when the hydraulic fluid passes through a damping valve (not shown) inside the cylinder, the gas chamber 7 partitioned off by the bladder 4 is compressed and expanded along with the inflow and outflow of hydraulic fluid in the reservoir chamber 8, and spring force in the hydraulic shock absorber arises according to the gas pressure in the gas chamber 7.
In this hydraulic shock absorber, the reservoir chamber 8 and gas chamber 7 are completely separated by the bladder 4, and the hydraulic fluid and gas do not mix, so the damping characteristics of the expanding and contracting action of the piston rod 2 can always remain stable according to design. It is also possible to maintain the same damping characteristics when the upper and lower ends of the hydraulic shock absorber are reversed in a so-called inverted placement.
However, the above-mentioned hydraulic shock absorber is configured such that the gas chamber 7 partitioned off by the bladder 4 is closed off from the exterior of the shock absorber, making it impossible to change the gas pressure in the interior from the gas pressure sealed during production of the hydraulic shock absorber.
Particularly, because of a configuration in which the bladder 4 is fastened to the periphery of the cylinder 1 by the clamp ring 5 and the gas chamber 7 is formed on the inner surface of the bladder 4, communication between the gas chamber 7 and the exterior of the shock absorber has been difficult, and it has also been difficult to adjust gas pressure by filling the gas chamber 7 with gas from the exterior or discharging gas to the exterior.
Therefore, when used as a hydraulic shock absorber for a motorcycle, for example, this hydraulic shock absorber has been impossible to adjust to optimum gas spring characteristics according to driver""s body weight, preferences, or the like. Another feature of this type of shock absorber is that when, for example, the components inside the cylinder are replaced, the inability to reduce the gas pressure in the gas chamber 7 causes the hydraulic fluid to be readily ejected to the exterior of the hydraulic shock absorber by the gas pressure, and makes it extremely difficult and inconvenient to replace the components.
Consequently, an object of this invention is to provide a hydraulic shock absorber in which adjustments can be made to the gas pressure in a gas chamber partitioned off by a bladder from the exterior of the shock absorber.
A further object of this invention is to provide a bladder mounting method in which a bladder for partitioning off a gas chamber can be appropriately mounted.
In order to achieve the above the objects, the invention provides a hydraulic shock absorber, comprising: a cylinder having an expandable and contactable piston rod; an outer casing disposed on the outside of the cylinder; a reservoir defined between the outer casing and the cylinder; a gas chamber formed by means of an elastically deformable bladder disposed in the reservoir, between the outer casing and the bladder, and filled with sealed gas and; a reservoir chamber formed between the bladder and the cylinder and communicated with the inside of the cylinder to guide hydraulic fluid; and a gas sealing valve provided to part of the outer casing and designed for opening and closing a flow conduit communicated with the gas chamber.
The invention further provides a method for manufacturing a hydraulic shock absorber comprising a cylinder, an outer casing disposed on the outside of the cylinder, and a reservoir provided with a gas chamber and a reservoir chamber and formed between the cylinder and the outer casing, comprising the steps of: fitting a pair of guide rings on the periphery of the cylinder having an expandable and contractible piston rod with a specific axial spacing and fixing the pair of guide rings thereto; inserting a flexible, cylindrical bladder from the outside of the cylinder and interlocking the upper and lower ends thereof with the pair of guide rings; inserting the cylinder in the outer casing along the axial direction with the bladder disposed on the outside, bringing the upper and lower ends of the bladder into close contact with the inner peripheral surface of the outer cylinder, and defining a gas chamber in the reservoir between the inner surface of the outer cylinder and the outer surface of the bladder; and forming a reservoir chamber, which is communicated with the inside of the cylinder and which guides the hydraulic fluid, between the inner surface of the bladder and the outer surface of the cylinder.
The details as well as other and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.